1. Field of the Invention
The present invention relates to semiconductor devices and, in particular, relates to a semiconductor device comprising a semiconductor die having a first plurality of bonding pads, and a lead frame having a second plurality of bonding pads, wherein the first bonding pads are connected to the second bonding pads by an automated wire bonding system.
2. Description of the Related Art
Advances in semiconductor processing methods continually provide modular semiconductor devices with increased circuit density and, thus, increased functionality. As a result, such devices are formed with reduced packaging sizes having increased numbers of conducting paths extending therefrom. Consequently, the problems associated with providing electrical connection to such devices are becoming increasingly apparent as will now be described in greater detail.
The typical semiconductor device comprises an extremely small semiconductor die encapsulated within a protective packaging material. In particular, the semiconductor die comprises electronic circuitry formed in a high density configuration. Such semiconductor dice include a plurality of circuit elements, such as transistors, diodes, resistors and capacitors, having sub-micron level dimensions. Furthermore, the circuit elements are electrically interconnected within the die in a preferred manner so as to provide the semiconductor die with a desired set of performance characteristics.
The typical semiconductor die is usually provided with a first plurality of wire bonding surfaces, otherwise referred to hereinbelow as bonding pads. In particular, the bonding pads are adapted to bond with first ends of a plurality of interconnecting conducting wires so that the first ends of the conducting wires are mechanically and electrically coupled to the first bonding pads. Additionally, the first bonding pads are arranged in a high density configuration on a surface of the die such that the pads are electrically coupled to specific circuit nodes within the die.
The typical semiconductor device further comprises a lead frame that provides the device with exposed leads that extend outside of the packaging material and that electrically couple with the circuit nodes of the encapsulated die. In particular, the lead frame usually includes a die mounting platform, otherwise known as a die paddle, which is adapted to fixedly support the die with respect to the lead frame. The lead frame of the typical semiconductor device further comprises a plurality of lead fingers which are disposed in a generally radial pattern around the die paddle so that the die mounted on the die paddle and the lead fingers are initially disposed in a generally common plane. Moreover, the lead fingers outwardly extend from first ends positioned at the interior of the packaging material adjacent the die paddle to second ends positioned at the exterior of the packaging material. Furthermore, a second plurality of bonding pads akin to the first bonding pads are usually located at the first ends of the lead fingers. Moreover, as will be described in greater detail below, the conducting wires are attached between the first and second bonding pads in a wire bonding process so as to electrically couple the first pads with the second pads.
Following the wire bonding process, the die is encapsulated within the packaging material which is typically formed with a rectangular shape. Furthermore, in addition to encapsulating the die, the packaging material also encapsulates the die paddle and the first ends of the lead fingers of the lead frame. However, the second ends of the lead fingers are positioned outside of the packaging material so that they are the exposed leads of the semiconductor device. Moreover, the exposed leads are typically bent so that each lead is positioned adjacent an exterior surface of the packaging material in a flush manner and so that the leads do not contact each other. Thus, since the conducting wires electrically couple the first and second bonding pads, the exposed leads are electrically coupled with the circuit nodes of the die.
Usually, each of the interconnecting conducting wires extending between the lead frame and the die are sequentially installed by an automated wire bonding system prior to encapsulation of the die. In particular, the typical wire bonding system is adapted to position the first end of a particular conducting wires adjacent the corresponding first bonding pad of the die in a flush manner. The wire bonding system is also adapted to bond the first end of the conducting wire to the corresponding first bonding pad so that the first end is fixedly attached thereto. Furthermore, the wire bonding system is adapted to position the second end of the conducting wires adjacent the corresponding second bonding pad of the lead frame in a flush manner and subsequently bond the second end thereto.
To determine the relative positions of the first and second bonding pads with respect to the wire bonding system, the typical automated wire bonding system utilizes an imaging device to obtain a digitized image of the lead frame having the die mounted thereto. In particular, the image is scanned by a processor which attempts to identify particular features of the die and lead frame. More particularly, the relative positions of the first bonding pads are determined by locating the die within the image. Furthermore, the positions of the second bonding pads of the lead frame are usually determined by identifying and locating the first end of at least one of the lead fingers of the lead frame within the image as disclosed in U.S. Pat. No. 5,350,106 to Fogal. Moreover, since the first ends of the lead fingers are fixedly positioned with respect to each other in a predefined manner, the positions of the remaining second bonding pads are determined by referencing the position of the first end of the at least one identified lead finger.
However, with the advent of increased circuit density, lead frames are required to accommodate greater numbers of lead fingers in higher density configurations. In particular, the increased density of the lead fingers requires their first ends and, thus, the second bonding pads formed thereon to be formed with reduced dimensions. Consequently, since it is generally not practical to provide relatively small bonding pads with a distinctive shape, the first ends of the lead fingers are often formed with nearly identical geometries. Thus, it is becoming increasingly difficult to correctly distinguish the first ends of the lead fingers of the lead frame from each other. As a result, automated wire bonding systems are increasingly having difficulties in identifying the lead fingers to connect the appropriate wirebonds.
For example, while attempting to identify the first end of the first lead finger of a high density lead frame, it is possible that the typical wire bonding system could mistakenly identify the first end of a neighboring second lead finger having a geometry similar to that of the first lead finger. Thus, the position of the first end of the first lead finger will be incorrectly determined. Furthermore, since the wire bonding system uses the position of the first end of the first lead finger to determine the positions of the first ends of the remaining lead fingers, the wire bonding system will incorrectly determine the positions of the first ends of the remaining lead fingers. Consequently, since the wire bonding system is unable to properly connect the first and second bonding pads together, the semiconductor device will not provide the desired electrical characteristics.
Another shortcoming of prior art wire bonding systems is that they utilize lead frames that provide an insufficient indication of the orientation of the lead frame. In particular, it is possible for the lead frame to be mistakenly oriented within the wire bonding system in a rotated manner such that the lead frame is rotated by 180 degrees about an axis that extends perpendicularly from the plane of the lead frame. Since the lead frame is often formed in a symmetrical manner with respect to such a rotation, this problem may be overlooked by an observer responsible for visually inspecting the orientation of the lead frame. Moreover, since the typical lead frame comprises a symmetrical shape with respect to the 180 degree rotation, the wire bonding system may not identify the incorrect orientation of the lead frame. Consequently, since the first bonding pads are often disposed on the die in an asymmetrical manner and since the interconnecting wires are often installed with an asymmetrical configuration, it is likely that considerable time and materials will be wasted by the wire bonding system in a futile attempt to electrically couple the die with the lead frame. Thus, since semiconductor devices formed in this manner lack the appropriate conducting paths that extend from the exposed leads, this problem results in increased failure rates, reduced production yields and increased production costs.
From the foregoing, therefore, it will be appreciated that there is a need for an improved automated wire bonding system. In particular, there is a need for the improved system to more reliably provide a high density semiconductor device with correctly extending conducting paths between exposed leads of a lead frame of the device to appropriate circuit nodes within an encapsulated semiconductor die of the device. Furthermore, there is a need for the system to utilize a lead frame that allows a user to more easily identify whether the lead frame is correctly oriented within the wire bonding system.
The aforementioned needs are satisfied by the present invention which, according to one aspect, comprises a semiconductor device that includes a semiconductor device having a first plurality of bonding pads disposed along a surface of the die. The semiconductor device further comprises a lead frame that includes a die paddle for supporting the semiconductor die, and a plurality of lead fingers having a second plurality of bonding pads formed thereon. The die paddle comprises a mounting region and at least one eyepoint feature that extends from the mounting region. The semiconductor die is mounted adjacent the mounting region of the die paddle so that the die is secured to the die paddle and so that the die does not extend over the at least one eyepoint feature. The semiconductor device further comprises a plurality of connecting wires that extend between the first and second bonding pads so as to provide electrically conducting paths therebetween.
In another aspect of the present invention, a method of electrically connecting a first plurality of bonding pads of a semiconductor die to a second plurality of bonding pads located on lead fingers of a lead frame of a semiconductor device comprises obtaining an image of the lead frame. The method further comprises identifying the location of an eyepoint feature formed on a die paddle of the lead frame adapted to receive the semiconductor die. The method further comprises determining the relative location of the second plurality of bonding pads from the identified location of the eyepoint feature located on the die paddle of the lead frame.
In a further aspect of the present invention, a wire bonding system is provided for wire bonding between a first plurality of bonding pads located on a surface of a die positioned on a die paddle of a lead frame and a second plurality of bonding pads located on lead fingers of a lead frame wherein the lead frame further comprises at least one eyepoint feature located on the die paddle. The system comprises an imaging device that obtains an image of the lead frame and a processor that receives the obtained image and evaluates the received image to determine the location of the at least one eyepoint feature located on the die paddle of the lead frame. The processor further determines the relative location of the second plurality of bonding pads from the determined location of the at least one eyepoint features. The system further comprises a wire bonding device that receives signals from the processor that attaches wire bonds between the first plurality of bonding pads and the second plurality of bonding pads as located by the processor from the image obtained by the imaging device.
In yet another aspect of the present invention, a lead frame comprises a die paddle having a plurality of outer lateral edges wherein the die paddle is adapted to receive a semiconductor die having a first plurality of bonding locations. The lead frame further comprises a plurality of lead fingers defining second bonding locations to which wire bonds are to be bonded in a desired pattern between the first plurality of bonding locations and a second plurality of bonding locations. The lead frame further comprises at least one eyepoint feature formed on a lateral edge of the die paddle so as to be visible when the die is mounted on the die paddle. The at least one eyepoint feature is fixedly positioned with respect to the second bonding locations so that the at least one eyepoint provides a point of reference from which the relative location of each of the second bonding locations with respect to an origin can be determined.
In another aspect of the present invention, a lead frame comprises a die paddle having a plurality of outer lateral edges wherein the die paddle is adapted to receive a semiconductor die. The lead frame further comprises a plurality of lead fingers and an orientation indicator formed on a lateral edge of the die paddle so as to be visible when the die is mounted on the die paddle. The orientation indicator extends in a direction corresponding to the orientation of the lead frame and enables a human observer to visually determine the orientation of the lead frame by observing the direction of extension of the orientation indicator.